1. Field of the Invention
The present invention relates to an instrumented capsule for the material irradiation tests, which is designed to monitor the irradiation history of specimens and simultaneously to control the environment during material irradiation tests.
2. Description of the Prior Art
There are several essential prerequisites to be solved for developing new types of nuclear reactors, such as next generation reactors. For example, it is necessary to qualify fuel and structural material performance that is compatible with the features of advanced reactors in the design stage. The important essential prerequisites for the development of nuclear reactors are the close examination into several phenomena related to irradiation in reactors, and the development of advanced materials with the resistance of irradiation aging.
In recent years, next generation light water reactors (NGLR), advanced pressurized water reactors (APWR) and liquid metal reactors (LMR) have been actively studied and developed, and, therefore, advanced structural materials and fuels which are compatible with the features of such reactors are under active study and development. When designing such reactors, it is necessary to evaluate and determine neutron resistance of conventional structural materials or advanced structural materials that may be used in the reactors.
Degradation in structural material performance caused by a reduction in a variety of mechanical properties of materials, due to irradiation of fast neutrons to the materials in a real nuclear reactor, is the most serious factor, resulting in a reduction in both integrity and life span of a nuclear power plant.
Therefore, material irradiation testing in research reactors for qualification of neutron resistance of structural materials is recognized as a very important test for developing advanced structural materials or for newly planning the essential components of reactors.
Such material irradiation test in research reactor has been typically performed with the use of various material testing facilities. Such a material testing facility includes an in-pile test section, a so-called xe2x80x9ccapsulexe2x80x9d. The capsule is the most important unit of the material testing facility, which houses specimens of a variety of target materials and is installed in an irradiation hole of the research reactor. The conventional capsules used in the material irradiation tests are classified into two types: instrumented capsules and non-instrumented capsules. The instrumented capsule has a connection channel through which control wires pass to connect the instruments of the capsule to a capsule control system installed outside the reactor pool, so it is possible to remotely control the test environments of the capsule, such as the inner temperature and atmosphere of the capsule, during a material irradiation test. On the contrary, the non-instrumented capsule does not have such a connection channel, so it is impossible to control the test environment of the capsule during a material irradiation test.
In other words, the non-instrumented capsule is an in-pile test unit lacking any means for remotely controlling the inner temperature and atmosphere of the capsule, so the irradiation temperature and atmosphere for target specimens housed in the capsule cannot be controlled. Therefore, the non-instrumented capsule, during a material irradiation test, does not provide a testing environment similar to the operational environments of real reactors. However, the instrumented capsule, related to the present invention, is an in-pile test section provided with an improvement in design of such a non-instrumented capsule. The construction of such instrumented capsules may be variously designed in accordance with irradiation test purposes, and may be equipped with various instruments, such as a thermocouple, a sub-heater, a pressure sensor, a strain gauge, and a dosimeter, in accordance with irradiation test purposes.
Uses of the instrumented capsules are wide, such that the capsules are preferably used in the qualification of nuclear fuel materials performance. However, the instrumented capsule related to the present invention is limitedly used in the qualification of performance of a variety of materials of reactor""s essential elements, other than fuel.
The main body 10 of an instrumented capsule 1 comprises heat media 13 collaterally acting as specimen holders at portions 14, specimens 2, dosimeters 29, and thermocouples 25, which are housed in a stainless steel shell 11 as shown in FIGS. 4a, 5a and 5b. The shell 11 of the capsule is a cylindrical body of about 1 m in length and 60 mm in outer diameter. The instrumented capsule also has a vacuum control pipe and heaters. The vacuum control pipe is used for controlling the pressure of helium gas in the capsule main body to control the degree of vacuum in said capsule main body, while the heaters are used for heating the specimens 2 in order to control the temperature of the specimens 2 during a material irradiation test. In the pool of a research reactor, a protection tube extends from the top end of the shell of the capsule installed in an irradiation hole, while a guide tube extends from the protection tube to a junction box. The protection tube and the guide tube, both air- and water-tight, guide the vacuum control pipe and the control wires while isolating them from coolant. The junction box connects the vacuum control pipe and the control wires to the capsule control system. Due to this unique construction of the instrumented capsule, it is possible to easily accomplish target irradiation temperature of specimens housed in the capsule, so an optimum material irradiation test under a testing environment similar to the operational environment of a real reactor may be accomplished.
The junction box has a role of connecting the capsule main body, installed in the irradiation hole of the reactor pool, and the capsule control system, installed at the upper portion of the research reactor, and connects the vacuum control pipe and a variety of control wires, such as a heater control wire and a thermocouple control wire, to the capsule control system. In such a case, the vacuum control pipe and the control wires extend from the interior of the shell of the capsule main body to the junction box guided by a protection tube and a guide tube. The junction box is an essential instrument necessarily used for detecting and controlling the specimen temperature during a material irradiation test. However, non-instrumented capsules do not have such a junction box. In the prior art, a junction box 110 of FIG. 14 has been used as the junction means. However, the conventional junction unit 110 has a complex construction with several problems whenever connecting the vacuum control pipe to the capsule control system within a limited space. The complex construction of the junction box 110 also causes difficulty in operation and fabrication of the instrumented capsules. In addition, the junction box 110 is quite heavy, thus sometimes overloading the flexible guide tube during a process of moving, loading or unloading the capsule main body in a research reactor. In such a case, the guide tube may be excessively bent at a radius of curvature larger than an allowable radius of curvature, thus causing severe problems.
Furthermore, The desired structural integrity of instrumented capsules and related systems for in-pile material irradiation tests must be accomplished. In an effort to secure such structural integrity of the instrumented capsules and related systems, it is necessary to perform a seismic analysis and structural analysis of the instrumented capsules and related systems in terms of dead loads, operational basic earthquake (OBE) and safe shutdown earthquake (SSE) in accordance with regulations of AMSE BandPV Code, Section III, Div. 1, Part NF. Particularly, since the irradiation hole of a reactor pool, in which the capsule main body is loaded, is located at a forced convectional area, the essential instruments of the capsule must be designed in consideration of several important design factors.
In the case of a typical research reactor in which coolant flows upward, the capsule for material irradiation tests is loaded into a vertical irradiation hole inside a reactor pool. However, due to forced-circulation-type coolant flow in such a research reactor, the capsule may be vibrated in the irradiation hole, so structural integrity of the capsule and related systems must be maintained. Therefore, a variety of capsule fixing devices and capsule loading/unloading methods compatible with the features of research reactors have been developed and used. The capsule fixing devices are used for fixing the capsules in the reactor pools during material irradiation tests, and the capsule loading/unloading methods are for loading and unloading of the capsule main bodies in the irradiation holes inside the reactor pools before and after the material irradiation tests.
In order to fix a capsule main body in an irradiation hole of a reactor pool before a material irradiation test, a grapple head 84, provided at the uppermost end of the capsule main body, as shown in FIG. 3, is rotated. When the grapple head 84 is rotated during the process of fixing the capsule main body, a torsion force is applied to the capsule main body. The capsule main body is thus stressed by the torsion force, and, in such a case, the guide pins 38a provided at the lower portion of the capsule main body may become overstressed leading to breakage. Therefore, the guide pins 38a must be designed such that they effectively endure such torsion force.
The inventors of the present invention thus have developed an instrumented capsule which houses specimens of various target materials and is equipped with a variety of instruments for controlling the temperatures of the specimens during a material irradiation test, and maintains desired structural integrity when the capsule is loaded into an irradiation hole of a research reactor pool, and which more effectively performs the material irradiation test in the research reactor.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an instrumented capsule for material irradiation tests in research reactors which is designed such that it houses specimens of target materials in its shell and easily and precisely controls the irradiation condition and the irradiation temperature, thus performing a material irradiation test under an optimum test environment, such as an irradiation temperature similar to the operational temperature of a real reactor.
Another object of the present invention is to provide an instrumented capsule for material irradiation tests in research reactors which has a guide spring means in addition to a conventional capsule fixing device, thus being stably held in an irradiation hole of a reactor pool while being prevented from excessive vibration caused by flow-induced vibration, and which does not interfere with adjacent structures during material irradiation tests, but safely performs the irradiation tests.
A further object of the present invention is to provide an instrumented capsule for material irradiation tests in research reactors which has a simple and safe junction box for simply and safely connecting a vacuum control pipe and a variety of control wires, such as a heater control wire and a thermocouple control wire, to a capsule control system installed outside a research reactor pool, and also which has a fixing unit capable of supporting the capsule main body in an irradiation hole of the reactor pool while maintaining the desired structural integrity of the capsule in the reactor pool where coolant flows upward, thus being compatible with the features of capsule loading/unloading methods.
In order to accomplish the above objects, the present invention provides an instrumented capsule for material irradiation tests in research reactors, including a capsule main body installed in a vertical irradiation hole of a research reactor pool, the capsule main body consisting of a shell opened at upper and lower ends thereof, a plurality of heat media set in the shell, a plurality of specimens set at a center and peripheral areas of each of the heat media, upper and lower reflectors installed on an upper end of an uppermost heat medium and under a lower end of a lowermost heat medium, respectively, a plurality of insulators interposed between adjacent heat media and positioned above and under the upper and lower reflectors, respectively, a spacer set in the shell at a position above an uppermost insulator, a spring seat installed above the spacer, a specimen compressing spring to bias the spring seat, thus compressing the specimens, a temperature control means for controlling a temperature inside the shell, the temperature control means consisting of a vacuum control pipe and a heater, a detecting means consisting of both a thermocouple used for detecting a temperature of the specimens and a dosimeter used for detecting a quantity of neutron radiation, upper and lower end plugs mounted to the upper and lower ends of the shell so as to seal the ends of the shell, and a lower fixing unit assembled with the lower end plug, and a connecting means for connecting the capsule main body to a capsule control system installed outside the reactor pool.
In the instrumented capsule, the shell of the capsule main body is a cylindrical body of about 0.6 m in diameter and 1 m in length. In order to stably and safely perform the material irradiation tests, an upper guide spring unit is fitted over the upper end of the shell so as to vertically place the capsule main body at the center of the vertical irradiation hole inside and minimize the influence of flow-induced vibration caused by forced-circulation-type coolant flow in the research reactor. The upper guide spring unit consists of upper and lower fixing rings, and a plurality of wire springs connected between the upper and lower fixing rings at regular intervals.
The temperature control means includes the vacuum control pipe and the heater. The vacuum control pipe is connected to the upper end of the capsule main body and controls the degree of vacuum in the capsule main body, thus controlling the quantity of transferred heat. The heater heats the specimens so as to control the temperature of the specimens. The control of the degree of vacuum and heater""s operation is performed in response to a signal indicative of specimens"" temperature detected by the thermocouples.
The connecting means includes a rigid protection tube connected to an upper end of the capsule main body so as to air- and water-tightly guide the vacuum control pipe and the control wires extending from the thermocouple and the heater inside the capsule main body while protecting the vacuum control pipe and the control wires, a flexible guide tube connected to the protection tube so as to guide the vacuum control pipe and the control wires, and a junction box connected to the guide tube pipe so as to connect the vacuum control pipe and the control wires to the capsule control system installed outside the reactor pool, thus acting as a medium which transmits signals to the capsule control system.
The lower fixing unit includes a lower end cap mounted to the lower end plug, a rod tip connected to a center of the lower end cap and vertically extending downward, with a plurality of locking blades formed on a lower portion of the rod tip and locked to a fixing slot formed on a receptacle provided in the irradiation hole, a stopper movably fitted over the rod tip, and a stopper spring fitted over the rod tip at a position between the stopper and the lower end cap, thus normally biasing the stopper downward in a vertical direction.
The stopper of the lower fixing unit includes a plurality of holes formed in the stopper so as to allow a coolant flowing from the bottom of the irradiation hole to smoothly flow upward through the stopper without being disturbed by the stopper, and a plurality of guide pins projected on a circumferential surface of the stopper in radial directions such that the guide pins come into contact with the inner surface of the irradiation hole when the capsule main body is installed in the irradiation hole.
The stopper also includes an annular ring that connects the outside ends of the guide pins so as to support the guide pins.